In recent years, there have been increasing demands for compact electronic components. The mainstream of coil components is shifting to a multilayer type which is suitable for size reduction.
Multilayer coil components obtained by co-firing magnetic ceramics and internal conductors have a problem that the internal stress caused by differences in thermal expansion coefficient between magnetic ceramic layers and internal conductor layers. These differences in thermal expansion coefficient can reduce magnetic properties of the magnetic ceramics, which can cause a reduction in impedance of the multilayer coil components and differences in impedance between the multilayer coil components.
In order to solve such a problem, an element proposed in Japanese Unexamined Patent Application Publication No. 2004-22798 (“Patent Document 1”) includes a multilayer impedance element in which a reduction or variation in impedance is prevented in such a manner that gaps, or openings are provided between magnetic ceramic layers and internal conductor layers. These gaps are formed by immersing a fired magnetic ceramic element in an acidic plating solution and the effect of stress due to the internal conductor layers on the magnetic ceramic layers is thereby eliminated. In the multilayer impedance element disclosed in Patent Document 1, the fired magnetic ceramic element is immersed in the plating solution, so that the plating solution penetrates the magnetic ceramic element through zones where the internal conductor layers are exposed at surfaces of the magnetic ceramic element, whereby the gaps are intermittently formed between the magnetic ceramic layers and the internal conductor layers. The formation of the gaps between the magnetic ceramic layers and the internal conductor layers causes the internal conductor layers to be thin; hence, the reduction of the percentage of each internal conductor layer in a space between the magnetic ceramic layers cannot be avoided.
Therefore, there is a problem in that the manufacture of products having low direct-current resistance is difficult. In particular, a compact product such as a product with a size of 1.0 mm×0.5 mm×0.5 mm or a product with a size of 0.6 mm×0.3 mm×0.3 mm needs to include thin magnetic ceramic layers. It is difficult with internal conductor layers and gaps provided between the magnetic ceramic layers, and with the internal conductor layers formed so as to have a large thickness. Therefore, there is a problem in that a reduction in direct-current resistance cannot be achieved or sufficient reliability cannot be secured because the internal conductor layers are likely to be broken by surges.